1. Field of the Invention
The present invention relates to a servomotor drive device to which the power source regeneration function to return regenerative energy generated during speed reduction of a servomotor connected to a rotating shaft of a moving part of an industrial robot to the AC power source side can be added, in accordance with operating conditions of the industrial robot.
2. Description of Related Art
Conventionally, in order to handle the regenerative energy generated during speed reduction of a servomotor, a servomotor drive device having a resistance regeneration function to consume the regenerative energy by a regenerative resistor and a servomotor drive device having the power source regeneration function to return the regenerative energy to the AC power source side are used.
The servomotor drive device having the resistance regeneration function has a converter having a plurality of diodes configured to convert an AC current from an AC power source into a DC current and to supply DC power to an inverter configured to convert DC power into AC power, and a regenerative resistor circuit having a switching element (for example, NPN transistor) and a regenerative resistor connected in series.
The servomotor drive device having a power source regeneration function has a converter that not only has a plurality of diodes but also the same number of switching elements as diodes, connected in parallel to the plurality of diodes, respectively.
The converter in the servomotor drive device having the resistance regeneration function has no switching element, and therefore, is more advantageous in downsizing of the device than the servomotor drive device having the power source regeneration function. On the other hand, the servomotor drive device having the power source regeneration function is capable of consuming a larger amount of regenerative energy than the servomotor drive device having the resistance regeneration function.
The regenerative energy generated during speed reduction of a servomotor connected to a rotating shaft of a moving part (for example, an arm) of an industrial robot is usually smaller in amount than the regenerative energy generated during speed reduction of a servomotor connected to a rotating shaft of a moving part of a machine tool or industrial machinery, and therefore, it is possible to deal with the regenerative energy by resistance regeneration. Consequently, when driving a servomotor connected to a rotating shaft of a moving part of an industrial robot, the servomotor drive device having the resistance regeneration function, which is advantageous in downsizing of the device, is generally used.
However, there is a case where the amount of the regenerative energy generated during speed reduction of a servomotor becomes larger than the amount of regenerative energy that can be handled by resistance regeneration, such as when a plurality of industrial robots is operated at the same time, when a servomotor connected to a rotating shaft of a moving part of an industrial robot and a servomotor connected to a rotating shaft of a moving part of a peripheral of the industrial robot are driven at the same time, and when a large-sized or high-speed industrial robot is operated. In this case, in order to make it possible to handle the generated regenerative energy, a servomotor drive device having both the resistance regeneration function and the power source regeneration function is used. A servomotor drive device having both the resistance regeneration function and the power source regeneration function has a converter having a plurality of diodes and switching elements in the same number as that of the plurality of diodes, and a regenerative resistor circuit.
Conventionally, as a servomotor drive device having both the resistance regeneration function and the power source regeneration function, a servomotor drive device, which performs only power source regeneration when the regenerative energy is equal to or less than a predetermined amount and performs both power source regeneration and resistance regeneration when the regenerative energy exceeds the predetermined amount, is proposed in Japanese Unexamined Utility Model Application Publication No. 62-26192 (JP62-26192U), Japanese Unexamined Patent Publication (Kokai) No. 2004-154961 (JP2004-154961A), and Japanese Unexamined Patent Publication (Kokai) No. 2011-101473 (JP2011-101473A) and a servomotor drive device, which exits power source regeneration and starts resistance regeneration when an power failure occurs, is proposed in Japanese Unexamined Patent Publication (Kokai) No. 2011-101474 (JP2011-101474).
When driving a servomotor connected to a rotating shaft of a moving part of an industrial robot, whether only the resistance regeneration function is sufficient to handle the regenerative energy or both the resistance regeneration function and the power source regeneration function are necessary to handle the regenerative energy is determined, in accordance with the operating conditions of the industrial robot, such as the number of industrial robots to be operated, the presence or absence of a peripheral to be used simultaneously with the industrial robot, and the size or speed of the industrial robot. That is, it is desirable to downsize the device by using a converter having a plurality of diodes and a regenerative resistor circuit, when only the resistance regeneration function is sufficient to handle the regenerative energy, and it is desirable to perform power source regeneration by using a converter having a plurality of diodes and switching elements in the same number as that of the diodes, and a regenerative resistor circuit, when both the resistance regeneration function and the power source regeneration function are necessary to handle the regenerative energy.
However, in the conventional servomotor drive device having both the resistance regeneration function and the power source regeneration function, a converter having a plurality of diodes and the same number of switching elements is provided in advance, and therefore, even when only the resistance regeneration function is sufficient to handle the regenerative energy, the converter having a plurality of diodes and the same number of switching elements is used. Consequently, in the conventional servomotor drive device having both the resistance regeneration function and the power source regeneration function, it is not possible to add the power source regeneration function in accordance with the operating conditions of the industrial robot.